Authorities have intensified operations against a splinter group from the Abu Sayyaf in the southern province of Sulu, Philippine Defence Secretary Delfin Lorenzana said on Wednesday, including an airstrike in parts of Jolo town on Tuesday. At least 21 people were killed and more than a hundred injured in two explosions at a Catholic Church in Sulu on Jan 27.

President Rodrigo Duterte’s “directive is to crush the Abu Sayyaf,” Lorenzana said. The military has been receiving reports of a possible terrorist attack in the province as early as August last year, he said.

Investigators are still looking at other suspects in the attack, including a Yemeni couple who may have carried out suicide bombings at the Church, according to the defence chief.

On Wednesday, two people died and four others injured when a grenade exploded in a mosque in Zamboanga City, the second explosion in the southern Mindanao island in 4 days.